This program is directed toward the total synthesis of endiandric acids, a family of recently discovered natural products with novel polycyclic structures and the investigation of their postulated "biogenesis". Two approaches are proposed: In the first scheme, stepwise, stereocontrolled and selective construction of the individual endiandric acids is proposed, whereas in the second scheme the construction of the postulated polyunsaturated precursors and the study of their collapse to endiandric acids is put forward. In both approaches a series of electrocyclic reactions serve as the key operations for the building of the polycyclic framework with complete stereospecificity. The complete natural chemical cascade of endiandric acids will be studied employing the envisioned synthetic materials. The final products and intermediates will be biologically investigated with regard to antitumor, antithrombotic, antiasthmatic, antihypertensive and other potentially useful activities.